WAN considerations

When the source and target are on the same subnet, generally a LAN environment, you should failover the IP address. However, if the source and target are on different subnets, generally a WAN environment, you should not failover the IP address. You have several options for handling WAN failover.

Scripting example using the BIND DNS client

Install the BIND DNS client on the target server, if it is not already installed.
Create a PATH statement on the target for the BIND directory to ensure that it runs every time the executable is called.
Update the Double-Take daemon on the target to use a domain account that has rights to modify BIND DNS. You will have to stop and restart the daemon for changes to the user account to take effect.
Create a failover script with the following command. Specify this script for post-failover.

nsupdate "dnsover"

Create a file called dnsover and add the following lines. This is the file called by your post-failover script.

# Substitute your source name, target name, and target IP address

update delete source_server_name.fully_qualified_domain.com

update add target_server_name.fully_qualified_domain.com 86400 A target_server_IP

send

Create a failback script with the following command. Specify this script for post-failback.

nsupdate "dnsback"

Create a file called dnsback and add the following lines. This is the file called by your post-failback script.

# Substitute your target name, source name, and source IP address

update delete target_server_name.fully_qualified_domain.com A

update add source_server_name.fully_qualified_domain.com 86400 A source_server_IP

send

When failover and failback occur, the failover and failback scripts will automatically trigger DNS updates.